Equal wavelength broadcasting



Jan. 15, 1935. H. HARBICH EQUAL` WAVELENGTH BROADCASTING Filed Sept. l1,1931 Y W 111' afney Patented Janl5, 1935 *UNITE-Dama `rinata EQUALwAvsLeNern sacapcasrnie Hans Harbich, Berlin-Steglitz, Germany, as-

' signor to C'. Lorenz Aktiengesellschaft,.Berlin- Tempelhcf, Germany, accmpariy `7 *Appliance september 11, 1931, serial-n0'. 562,425 1In'Germany September 13, `19.3,@

" 4' claims. (ci. 25e-f2) f,

This invention relates generally to radio trans` same wavelength 'aresupplied from'a cer`itralv station withl afundamental frequency which ismultiplied at the transmitters to form the carrier frequency; and` inthe other of which, synchronization of the transmitting apparatus ateach of the different stations is effected by local means. Both thesearrangements, however, result in disturbed areas between the`transmitting stations in which the magnitudes of said disturbed areasare dependent on the magnitudes of thedegree of control of the apparatusin the individual transmitting stations.

According to the present invention,` it is proposed to limit the degreeof modulation control, so that it never exceeds a predetermined value,by automatically regulating the amplifiers in each transmitting station.

Another object ofthe invention is to keep the size of the disturbed areaconstant, this size being dependent solely upon the degree of modulationchosen` for the individual transmitting stations.

A further object of the invention is to position the disturbed area overa predetermined locality between the transmitting stations.

An embodiment of the invention is illustrated in the accompanyingdrawing, wherein: Y

Fig. 1 represents the disturbed area between two transmitting stationsusing earlier methods of modulation;

Fig. 2 represents the disturbed area between two transmitting stationsusing a method of modulation according to the present invention;

Fig. 3 is a schematic representation of two transmitting stations, eachreceiving the same program from a microphone in a central station andoperating on the same wavelength.

In Figs. 1 and 2, A andV B are broadcasters simultaneously transmittingon equal wavelengths. The hatched area between the two stationsrepresents the disturbed area where the signals of each station aredistorted.

v In Fig. 3, where a schematic broadcasting systemv employing theinvention is shown, two broadcast stations and a central station areindicated as A, B and C, respectively. At the central station C there isa microphone M and an ampliner V. At each of the broadcasting stationsthere is a modulation-amplifier MV, an amplitude-liiniter F, and atransmitter S, together with the necessary antennafground connection andconnecting land lines to the central station C. Y

" In the event of modulation, the disturbed area between-the twotransmitting stationsemittinguwaves of the same frequencywill bei'very/large, in fact, comprising' practically -the entire territorybetween and around said transmitting stations.

However, if the modulation be reduced to 30% the ratio of the fieldstrengths considered at a predetermined point may amount to 1: 2 withoutany distortion becoming noticeable.

If the modulation be still further reduced to 20%, a ratio of eldstrengths amounting to 1: 1% would be permissible at the predeterminedpoint.

For example, assuming transmitting stations.

Thus, a maximum limit for the percentage modulation is determined byexperiment which gives a minimum disturbed area. This percentage whendetermined is used as a fixed maximum above which themodulation-amplifier MV (Fig. 3) Will not pass energy to the transmitterS. Therefore, the modulation-amplifier functions merely to preventexcessive modulation. The maximum percentage modulation of theindividual broadcasters is so limited by the automatic regulation of MV,that the size of the disturbed area between broadcast stations emittingwaves of the same frequency is kept a constant minimum.

The location of the disturbed area between the broadcasters depends uponthe ratio of the `amplitudes of the carrier frequency of the individualtransmitters.

If the broadcasters do not possess the same amplitude of carrierfrequency, the disturbed area is shifted toward the This area can,

ThllS limits of amplitude fcr the carrier frequencies are determined,which place the disturbed area where itgives the least trouble tobroadcast re- CGlVeI'S The maximum amplitude of the individualbroadcaster is so limited by the automatic regulation of theamplitude-limiters F (Fig. 3) that the disturbed area is positioned overa predetermined locality.

In carrying out this method of control over the disturbed area betweenbroadcasters, care must be taken that the percentagel modulation of bothtransmitters is the same, since it can be easily proved by experimentthat in such a case the smallest area of distortion will occur betweenthe broadcasters. This is further achieved through devices for limitingthe fieldl strength which will take care that the transmission eiiciencyof the broadcaster` is the same, even though there is a differentvamplitudejof rthe carrier frequency. It is not necessary to describedevices, such as variable antennacouplers, for limiting the transmissioneciency of v a broadcaster, since these arrangements are well` ,from-twotransmittinggsta-t-ions which comprises the following steps,modulating-and amplifying signals, andadjusting'the degree of:m0dulation`s o as to reduce to a minimum the area ofthe interference in thereception froin'said stations.

2. Method according to claim 1 characterized by the step of adjustingthe amplitude of the carrier frequencies to determine the location ofsaid interference.

3. Method of equal wavelength broadcasting from two transmittingstations comprising the following steps, modulating Aand amplifyingsignals at` said stations, broadcastingsaid-signals from saidstations,adjusting the'degreeA of modulation to a point for reducing toa minimum `the area of the interference in the reception vfrom saidstations, and determining the location ,ting` stationY ,the` degree-of Ymodulation tol a point for reducing to a minimumythe area of 'theainter.-

ference in ythe'freception Afrom said stations; and

determining.` the location of. said' interference by;adjustingtheamplituderatiossof the unmodiulated transmittersl atx-said transmittingstations.

HANS HARBICI-..I

